The drop-on-demand ink-jet head is known as an ink-jet head that can eject, in response to the input signal, required amounts of ink droplets only when they are needed to print on the medium. In particular, extensive research is being undertaken on the piezoelectric (piezo) drop-on-demand ink-jet head as it is capable of well-controlled discharge of a wide variety of inks. The piezo drop-on-demand ink-jet head generally includes an ink supply channel; a plurality of ink chambers with a nozzle, which are connected to the ink supply channel; and piezoelectric elements for applying a pressure to the ink filling the ink chambers.
In such a piezo drop-on-demand ink-jet head, piezoelectric elements deform by application of a drive voltage, whereby a pressure is applied to the ink in ink chambers, causing ink droplets to be discharged from nozzles. Broadly, there are three types of piezo drop-on-demand ink-jet head according to the manner in which the piezoelectric element deforms: shear mode, push mode, and bend mode. In particular, because of its ability to produce high power at low voltage, the bend-mode piezo ink-jet head that uses multilayer piezoelectric elements is expected to be further developed for use in the manufacturing of electric devices using highly viscous ink, such as manufacturing of organic EL display panels and liquid crystal panels.
Ink-jet heads sometimes encounter the problem of failing to accurately discharge ink droplets due to air inclusion or nozzle clogging. To overcome this drawback, there have been proposed techniques in which ink is allowed to circulate through the ink-jet head, i.e., fed into and discharged from ink chambers such that air inclusion and nozzle clogging are reduced (see, e.g., Patent Literatures 2 to 6).
Also proposed are ink-circulating ink-jet heads in which piezoelectric elements are placed inside respective ink chambers (see, e.g., Patent Literatures 7 and 8).
FIG. 1 is a sectional view of an ink-circulating ink-jet head disclosed by Patent Literatures 7 and 8. As illustrated in FIG. 1, ink-jet head 1 of Patent Literatures 7 and 8 includes ink chambers 10, ink supply channel 11 in which the ink to be supplied to ink chambers 10 flows, and ink discharge channel 12 in which the ink discharged from ink chamber 10 flows.
Ink chamber 10 is composed of nozzle plate 20 which constitutes a bottom surface of ink chamber 10 and has nozzle 21; piezo-mounting plate 30 which constitutes a top surface of ink chamber 10 and to which piezoelectric element 31 is secured; and partition wall 40 which constitutes a side surface of ink chamber 10.
Ink inlet opening 33 for supplying ink to ink chamber 10 from ink supply channel 11 and ink outlet opening 35 for discharging ink from ink chamber 10 to ink discharge channel 12 are formed in piezo-mounting plate 30.
Ink flows from supply channel 11 into ink discharge channel 12 through ink chamber 10. Thus, new ink is continuously supplied to ink chamber 10. Continuously supplying new ink to ink chamber 10 avoids possible ink discharge failure caused by ink stagnation or air inclusion inside ink chamber 10.
Application of a drive voltage to piezoelectric element 31 in ink-jet head 1 having such a structure causes piezoelectric element 31 to expand, resulting in the application of a force to the ink inside ink chamber 10 in discharge direction. A portion of ink that has received the force is then discharged from nozzle 21.
Although the ink-circulating ink-jet head can avoid ink stagnation or air inclusion inside ink chambers, it has been said that further enhancement of ink discharge power is impossible with this type of ink-jet head due to the presence of two force-releasing routes (ink inlet opening 33 and ink outlet opening 25) from which the force generated by driving the piezoelectric element is released.